The present invention, in some embodiments thereof, relates to wireless communication networks and, more particularly, but not exclusively, to a method and an apparatus for switching between a plurality of antennas during a communication session.
A number of standards have been developed in recent years for providing wireless network access. These include such standards as the IEEE 802.16 family (i.e., WirelessMAN, also known as worldwide interoperability for microwave access (WiMAX), HIPERMAN, wireless broadband (WiBro), and 3rd generation partnership project (3GPP) systems generally, which the standards thereof are incorporated herein by reference. These standards provide a wireless network access to remote users via client terminals, such as customer-provided equipments (CPEs), for example WiMAX or Wi-Fi modems. These CPEs are usually located at a subscribers premises and connected with carriers telecommunication channels at the demarcation point.
During the last decade, the requirement for CPEs that supports high speed data traffic, such as videoconference, file streaming, video-on-demand, and the interactive video game, has increased. As commonly known, the data rate of a wireless channel equals to a product of the wireless channel's spectrum width and the spectrum efficiency. As the frequency resource is limited, improving the spectrum efficiency of the adopted technology is a feasible solution.
CPEs which use multiple antennas to improve the performance of radio communication systems, such as multiple input and multiple-output (MIMO) based CPEs, provide a promising solution for improving the spectrum efficiency. However, these antennas, as other antennas, encounter communication difficulties such as fading conditions. If fading conditions are significant, and compensation cannot be made at the client terminal, the informational content of the data cannot be successfully recovered and the quality of service (QoS) decreases.
Various diversity schemes have been developed and utilized to compensate for fading. Generally, diversity schemes increase the redundancy of data throughput that is sent to the client terminals. Increasing the time redundancy of the data, for instance, increases the likelihood that the informational content of the data may be recovered when received at a receiving station. Another developed scheme is space diversity with multiple antennas. When space diversity is created, data that is communicated by a sending station to a receiving station is communicated by way of different communication paths via different antennas. Fading conditions along the separate communication paths might differ, and fading of data communicated upon one communication path to prevent its successful delivery might be compensated for by successful delivery of the data communicated along another communication path.
Compensation can also be made for fading conditions by increasing the power level at which data is communicated by a transmitting station. By increasing the power of the transmitted data, data values, of increased power levels, are more likely to be detectable at a receiving station, even when communicated upon a fading channel.
An example for compensating for the effects of fading is provided in U.S. Patent Application Publication Number 2005/0245280 published on Nov. 3, 2005. This patent application describes a method in which an analysis is made at a receiving station, such as through channel estimation by a channel estimator, of communication conditions on different sub-channels, defined by different communication paths upon which data streams are communicated to the receiving station from different transmit antenna transducers. Power controllers generate power change requests responsive to the channel estimations. The power change requests are returned to a sending station by way of a feedback channel. In addition, the power levels at which data is transmitted from different transmit antennas is correspondingly changed.